1. Field of the Invention
The present invention relates to a method for generating nominal position values for a position control loop of a numerically continuous-path controlled machine. The subject of the present invention is also a circuit arrangement for generating nominal position values for a position control loop of a numerically continuous-path controlled machine.
2. Description of the Related Art
In numerically continuous-path controlled machine tools or robots, the production of nominal position values is done as nominal value specifications or command variables for the position control loops of the various drive mechanisms, typically in interpolator units located upstream. For that purpose, the desired geometrical axis motion functions and speed profiles are specified to the interpolator units on the input side. On the output side, the interpolator unit furnishes discrete trains of nominal position values or scanned values on a path curve. The nominal position values are output at a defined, typically fixed interpolator clock rate fIPO as command variables to the downstream position control loop. In addition, the nominal position values produced by the interpolator unit, before being transmitted to the position control loop, are also filtered in a nominal position value filter, which as a rule takes the form of digital low-pass filtering. This is done so that the axis drive systems will not induce undesired natural oscillations in the machine, which might lower the quality of the machining.
In conjunction with such variants for generating nominal position values in numerically continuous-path controlled machines, reference may be made for instance to German Patent Disclosure DE 43 03 090 A1.
The filtering in the nominal position value filter is typically designed such that in the spectrum of nominal position values or command variables transmitted to the position control loop, as much as possible no frequencies are located in the range of the resonant frequency fRES of the applicable machine, or in a corresponding resonant frequency band BRES. Otherwise, the natural oscillations in the machine axes would result in impaired surface quality of the machined workpiece. By way of a band limitation of the command variables, in the form of low-pass filtration, it is therefore assured that the applicable nominal position value filter will block those components of the frequency that are greater than a suitably selected useful machine frequency fN. The corresponding useful machine frequency fN of the nominal position value filter is selected as a function of the applicable resonant frequency fRES or resonant frequency band BRES.
In the event of especially low resonant frequencies fRES, such as fRES≈20 Hz, however, designing the digital nominal position value filter requires increasing computation effort and expense to achieve the desired filtering action.
It is therefore an object of the present invention to disclose a method and a circuit arrangement for generating nominal position values for a position control loop of a numerically continuous-path controlled machine by way of which, for the most various types of machine and without major effort or expense, path errors that result from induced natural oscillations of the machine can be avoided.
This object is attained by a method for generating nominal position values for a position control loop of a numerically continuous-path controlled machine. The method includes presetting nominal position values with a defined interpolator clock rate, digitally filtering the preset nominal position values and transmitting the digitally filtered nominal position values to a position control loop, which with them controls motion of a machine on a path curve at a defined position control clock rate. Adjusting the digitally filtering nominal position values as a function of dynamic characteristics of the machine and adjusting an interpolator clock rate as a function of the dynamic characteristics of the machine.
This object is also attained by a circuit arrangement for generating nominal position values for a position control loop of a numerically continuous-path controlled machine. The circuit arrangement includes an interpolator unit for presetting nominal position values with a defined interpolator clock rate, a nominal position value filter for digital filtration of the nominal position values preset by the interpolator unit. A position control loop, which processes the digitally filtered nominal position values in such a way that by way of them a motion of a machine on a path curve is controllable at a defined position control clock rate, wherein along with the nominal position value filter, the interpolator clock rate is also adjusted as a function of dynamic characteristics of the machine.
In the present invention, it is now not primarily the nominal position value filter employed that is adapted to the applicable dynamic characteristics of the machinexe2x80x94and in particular its resonant frequency; instead, it is the applicable interpolator clock rate or interpolator clock duration that is adjusted in a targeted way as a function of the dynamic characteristics of the machine, in order to avoid the inducement of undesired natural oscillations. In this way, the computation effort and expense otherwise required for the same filtering action in the nominal position value filter is avoided.
Since the provisions according to the present invention, in the case of low resonant frequencies, essentially represent an increase in the interpolator clock durations or a decrease in the interpolator clock rates, a correspondingly greater computation power for other tasks is now available in the interpolator unit as well. This includes for instance generating nominal position values for still other machine axes, etc.
It also proves advantageous to use a fine interpolator between the nominal position value filter and the position control loop, in the method and circuit arrangement according to the present invention. By way of the fine interpolator, scanned values on the path curve are generated in the time pattern in which the downstream position control loop needs them. It is especially advantageous in this respect that by the fine interpolator, the interpolator clock rate is decoupled from the downstream position control loop, and in particular from the position control clock rate; as a rule, however, there is a fixed ratio between the position control clock rate and the interpolator clock rate.